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      1 //===-- llvm/GlobalValue.h - Class to represent a global value --*- C++ -*-===//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 //
     10 // This file is a common base class of all globally definable objects.  As such,
     11 // it is subclassed by GlobalVariable, GlobalAlias and by Function.  This is
     12 // used because you can do certain things with these global objects that you
     13 // can't do to anything else.  For example, use the address of one as a
     14 // constant.
     15 //
     16 //===----------------------------------------------------------------------===//
     17 
     18 #ifndef LLVM_IR_GLOBALVALUE_H
     19 #define LLVM_IR_GLOBALVALUE_H
     20 
     21 #include "llvm/IR/Constant.h"
     22 #include "llvm/IR/DerivedTypes.h"
     23 #include <system_error>
     24 
     25 namespace llvm {
     26 
     27 class Comdat;
     28 class PointerType;
     29 class Module;
     30 
     31 namespace Intrinsic {
     32   enum ID : unsigned;
     33 }
     34 
     35 class GlobalValue : public Constant {
     36   GlobalValue(const GlobalValue &) = delete;
     37 public:
     38   /// @brief An enumeration for the kinds of linkage for global values.
     39   enum LinkageTypes {
     40     ExternalLinkage = 0,///< Externally visible function
     41     AvailableExternallyLinkage, ///< Available for inspection, not emission.
     42     LinkOnceAnyLinkage, ///< Keep one copy of function when linking (inline)
     43     LinkOnceODRLinkage, ///< Same, but only replaced by something equivalent.
     44     WeakAnyLinkage,     ///< Keep one copy of named function when linking (weak)
     45     WeakODRLinkage,     ///< Same, but only replaced by something equivalent.
     46     AppendingLinkage,   ///< Special purpose, only applies to global arrays
     47     InternalLinkage,    ///< Rename collisions when linking (static functions).
     48     PrivateLinkage,     ///< Like Internal, but omit from symbol table.
     49     ExternalWeakLinkage,///< ExternalWeak linkage description.
     50     CommonLinkage       ///< Tentative definitions.
     51   };
     52 
     53   /// @brief An enumeration for the kinds of visibility of global values.
     54   enum VisibilityTypes {
     55     DefaultVisibility = 0,  ///< The GV is visible
     56     HiddenVisibility,       ///< The GV is hidden
     57     ProtectedVisibility     ///< The GV is protected
     58   };
     59 
     60   /// @brief Storage classes of global values for PE targets.
     61   enum DLLStorageClassTypes {
     62     DefaultStorageClass   = 0,
     63     DLLImportStorageClass = 1, ///< Function to be imported from DLL
     64     DLLExportStorageClass = 2  ///< Function to be accessible from DLL.
     65   };
     66 
     67 protected:
     68   GlobalValue(Type *Ty, ValueTy VTy, Use *Ops, unsigned NumOps,
     69               LinkageTypes Linkage, const Twine &Name, unsigned AddressSpace)
     70       : Constant(PointerType::get(Ty, AddressSpace), VTy, Ops, NumOps),
     71         ValueType(Ty), Linkage(Linkage), Visibility(DefaultVisibility),
     72         UnnamedAddr(0), DllStorageClass(DefaultStorageClass),
     73         ThreadLocal(NotThreadLocal), IntID((Intrinsic::ID)0U), Parent(nullptr) {
     74     setName(Name);
     75   }
     76 
     77   Type *ValueType;
     78   // Note: VC++ treats enums as signed, so an extra bit is required to prevent
     79   // Linkage and Visibility from turning into negative values.
     80   LinkageTypes Linkage : 5;   // The linkage of this global
     81   unsigned Visibility : 2;    // The visibility style of this global
     82   unsigned UnnamedAddr : 1;   // This value's address is not significant
     83   unsigned DllStorageClass : 2; // DLL storage class
     84 
     85   unsigned ThreadLocal : 3; // Is this symbol "Thread Local", if so, what is
     86                             // the desired model?
     87   static const unsigned GlobalValueSubClassDataBits = 19;
     88 
     89 private:
     90   // Give subclasses access to what otherwise would be wasted padding.
     91   // (19 + 3 + 2 + 1 + 2 + 5) == 32.
     92   unsigned SubClassData : GlobalValueSubClassDataBits;
     93 
     94   friend class Constant;
     95   void destroyConstantImpl();
     96   Value *handleOperandChangeImpl(Value *From, Value *To, Use *U);
     97 
     98 protected:
     99   /// \brief The intrinsic ID for this subclass (which must be a Function).
    100   ///
    101   /// This member is defined by this class, but not used for anything.
    102   /// Subclasses can use it to store their intrinsic ID, if they have one.
    103   ///
    104   /// This is stored here to save space in Function on 64-bit hosts.
    105   Intrinsic::ID IntID;
    106 
    107   unsigned getGlobalValueSubClassData() const {
    108     return SubClassData;
    109   }
    110   void setGlobalValueSubClassData(unsigned V) {
    111     assert(V < (1 << GlobalValueSubClassDataBits) && "It will not fit");
    112     SubClassData = V;
    113   }
    114 
    115   Module *Parent;             // The containing module.
    116 public:
    117   enum ThreadLocalMode {
    118     NotThreadLocal = 0,
    119     GeneralDynamicTLSModel,
    120     LocalDynamicTLSModel,
    121     InitialExecTLSModel,
    122     LocalExecTLSModel
    123   };
    124 
    125   ~GlobalValue() override {
    126     removeDeadConstantUsers();   // remove any dead constants using this.
    127   }
    128 
    129   unsigned getAlignment() const;
    130 
    131   bool hasUnnamedAddr() const { return UnnamedAddr; }
    132   void setUnnamedAddr(bool Val) { UnnamedAddr = Val; }
    133 
    134   bool hasComdat() const { return getComdat() != nullptr; }
    135   Comdat *getComdat();
    136   const Comdat *getComdat() const {
    137     return const_cast<GlobalValue *>(this)->getComdat();
    138   }
    139 
    140   VisibilityTypes getVisibility() const { return VisibilityTypes(Visibility); }
    141   bool hasDefaultVisibility() const { return Visibility == DefaultVisibility; }
    142   bool hasHiddenVisibility() const { return Visibility == HiddenVisibility; }
    143   bool hasProtectedVisibility() const {
    144     return Visibility == ProtectedVisibility;
    145   }
    146   void setVisibility(VisibilityTypes V) {
    147     assert((!hasLocalLinkage() || V == DefaultVisibility) &&
    148            "local linkage requires default visibility");
    149     Visibility = V;
    150   }
    151 
    152   /// If the value is "Thread Local", its value isn't shared by the threads.
    153   bool isThreadLocal() const { return getThreadLocalMode() != NotThreadLocal; }
    154   void setThreadLocal(bool Val) {
    155     setThreadLocalMode(Val ? GeneralDynamicTLSModel : NotThreadLocal);
    156   }
    157   void setThreadLocalMode(ThreadLocalMode Val) {
    158     assert(Val == NotThreadLocal || getValueID() != Value::FunctionVal);
    159     ThreadLocal = Val;
    160   }
    161   ThreadLocalMode getThreadLocalMode() const {
    162     return static_cast<ThreadLocalMode>(ThreadLocal);
    163   }
    164 
    165   DLLStorageClassTypes getDLLStorageClass() const {
    166     return DLLStorageClassTypes(DllStorageClass);
    167   }
    168   bool hasDLLImportStorageClass() const {
    169     return DllStorageClass == DLLImportStorageClass;
    170   }
    171   bool hasDLLExportStorageClass() const {
    172     return DllStorageClass == DLLExportStorageClass;
    173   }
    174   void setDLLStorageClass(DLLStorageClassTypes C) { DllStorageClass = C; }
    175 
    176   bool hasSection() const { return !StringRef(getSection()).empty(); }
    177   // It is unfortunate that we have to use "char *" in here since this is
    178   // always non NULL, but:
    179   // * The C API expects a null terminated string, so we cannot use StringRef.
    180   // * The C API expects us to own it, so we cannot use a std:string.
    181   // * For GlobalAliases we can fail to find the section and we have to
    182   //   return "", so we cannot use a "const std::string &".
    183   const char *getSection() const;
    184 
    185   /// Global values are always pointers.
    186   PointerType *getType() const { return cast<PointerType>(User::getType()); }
    187 
    188   Type *getValueType() const { return ValueType; }
    189 
    190   static LinkageTypes getLinkOnceLinkage(bool ODR) {
    191     return ODR ? LinkOnceODRLinkage : LinkOnceAnyLinkage;
    192   }
    193   static LinkageTypes getWeakLinkage(bool ODR) {
    194     return ODR ? WeakODRLinkage : WeakAnyLinkage;
    195   }
    196 
    197   static bool isExternalLinkage(LinkageTypes Linkage) {
    198     return Linkage == ExternalLinkage;
    199   }
    200   static bool isAvailableExternallyLinkage(LinkageTypes Linkage) {
    201     return Linkage == AvailableExternallyLinkage;
    202   }
    203   static bool isLinkOnceODRLinkage(LinkageTypes Linkage) {
    204     return Linkage == LinkOnceODRLinkage;
    205   }
    206   static bool isLinkOnceLinkage(LinkageTypes Linkage) {
    207     return Linkage == LinkOnceAnyLinkage || Linkage == LinkOnceODRLinkage;
    208   }
    209   static bool isWeakAnyLinkage(LinkageTypes Linkage) {
    210     return Linkage == WeakAnyLinkage;
    211   }
    212   static bool isWeakODRLinkage(LinkageTypes Linkage) {
    213     return Linkage == WeakODRLinkage;
    214   }
    215   static bool isWeakLinkage(LinkageTypes Linkage) {
    216     return isWeakAnyLinkage(Linkage) || isWeakODRLinkage(Linkage);
    217   }
    218   static bool isAppendingLinkage(LinkageTypes Linkage) {
    219     return Linkage == AppendingLinkage;
    220   }
    221   static bool isInternalLinkage(LinkageTypes Linkage) {
    222     return Linkage == InternalLinkage;
    223   }
    224   static bool isPrivateLinkage(LinkageTypes Linkage) {
    225     return Linkage == PrivateLinkage;
    226   }
    227   static bool isLocalLinkage(LinkageTypes Linkage) {
    228     return isInternalLinkage(Linkage) || isPrivateLinkage(Linkage);
    229   }
    230   static bool isExternalWeakLinkage(LinkageTypes Linkage) {
    231     return Linkage == ExternalWeakLinkage;
    232   }
    233   static bool isCommonLinkage(LinkageTypes Linkage) {
    234     return Linkage == CommonLinkage;
    235   }
    236 
    237   /// Whether the definition of this global may be discarded if it is not used
    238   /// in its compilation unit.
    239   static bool isDiscardableIfUnused(LinkageTypes Linkage) {
    240     return isLinkOnceLinkage(Linkage) || isLocalLinkage(Linkage) ||
    241            isAvailableExternallyLinkage(Linkage);
    242   }
    243 
    244   /// Whether the definition of this global may be replaced by something
    245   /// non-equivalent at link time. For example, if a function has weak linkage
    246   /// then the code defining it may be replaced by different code.
    247   static bool mayBeOverridden(LinkageTypes Linkage) {
    248     return Linkage == WeakAnyLinkage || Linkage == LinkOnceAnyLinkage ||
    249            Linkage == CommonLinkage || Linkage == ExternalWeakLinkage;
    250   }
    251 
    252   /// Whether the definition of this global may be replaced at link time.  NB:
    253   /// Using this method outside of the code generators is almost always a
    254   /// mistake: when working at the IR level use mayBeOverridden instead as it
    255   /// knows about ODR semantics.
    256   static bool isWeakForLinker(LinkageTypes Linkage)  {
    257     return Linkage == WeakAnyLinkage || Linkage == WeakODRLinkage ||
    258            Linkage == LinkOnceAnyLinkage || Linkage == LinkOnceODRLinkage ||
    259            Linkage == CommonLinkage || Linkage == ExternalWeakLinkage;
    260   }
    261 
    262   bool hasExternalLinkage() const { return isExternalLinkage(Linkage); }
    263   bool hasAvailableExternallyLinkage() const {
    264     return isAvailableExternallyLinkage(Linkage);
    265   }
    266   bool hasLinkOnceLinkage() const {
    267     return isLinkOnceLinkage(Linkage);
    268   }
    269   bool hasLinkOnceODRLinkage() const { return isLinkOnceODRLinkage(Linkage); }
    270   bool hasWeakLinkage() const {
    271     return isWeakLinkage(Linkage);
    272   }
    273   bool hasWeakAnyLinkage() const {
    274     return isWeakAnyLinkage(Linkage);
    275   }
    276   bool hasWeakODRLinkage() const {
    277     return isWeakODRLinkage(Linkage);
    278   }
    279   bool hasAppendingLinkage() const { return isAppendingLinkage(Linkage); }
    280   bool hasInternalLinkage() const { return isInternalLinkage(Linkage); }
    281   bool hasPrivateLinkage() const { return isPrivateLinkage(Linkage); }
    282   bool hasLocalLinkage() const { return isLocalLinkage(Linkage); }
    283   bool hasExternalWeakLinkage() const { return isExternalWeakLinkage(Linkage); }
    284   bool hasCommonLinkage() const { return isCommonLinkage(Linkage); }
    285 
    286   void setLinkage(LinkageTypes LT) {
    287     if (isLocalLinkage(LT))
    288       Visibility = DefaultVisibility;
    289     Linkage = LT;
    290   }
    291   LinkageTypes getLinkage() const { return Linkage; }
    292 
    293   bool isDiscardableIfUnused() const {
    294     return isDiscardableIfUnused(Linkage);
    295   }
    296 
    297   bool mayBeOverridden() const { return mayBeOverridden(Linkage); }
    298 
    299   bool isWeakForLinker() const { return isWeakForLinker(Linkage); }
    300 
    301   /// Copy all additional attributes (those not needed to create a GlobalValue)
    302   /// from the GlobalValue Src to this one.
    303   virtual void copyAttributesFrom(const GlobalValue *Src);
    304 
    305   /// If special LLVM prefix that is used to inform the asm printer to not emit
    306   /// usual symbol prefix before the symbol name is used then return linkage
    307   /// name after skipping this special LLVM prefix.
    308   static StringRef getRealLinkageName(StringRef Name) {
    309     if (!Name.empty() && Name[0] == '\1')
    310       return Name.substr(1);
    311     return Name;
    312   }
    313 
    314 /// @name Materialization
    315 /// Materialization is used to construct functions only as they're needed. This
    316 /// is useful to reduce memory usage in LLVM or parsing work done by the
    317 /// BitcodeReader to load the Module.
    318 /// @{
    319 
    320   /// If this function's Module is being lazily streamed in functions from disk
    321   /// or some other source, this method can be used to check to see if the
    322   /// function has been read in yet or not.
    323   bool isMaterializable() const;
    324 
    325   /// Make sure this GlobalValue is fully read. If the module is corrupt, this
    326   /// returns true and fills in the optional string with information about the
    327   /// problem.  If successful, this returns false.
    328   std::error_code materialize();
    329 
    330 /// @}
    331 
    332   /// Return true if the primary definition of this global value is outside of
    333   /// the current translation unit.
    334   bool isDeclaration() const;
    335 
    336   bool isDeclarationForLinker() const {
    337     if (hasAvailableExternallyLinkage())
    338       return true;
    339 
    340     return isDeclaration();
    341   }
    342 
    343   /// Returns true if this global's definition will be the one chosen by the
    344   /// linker.
    345   bool isStrongDefinitionForLinker() const {
    346     return !(isDeclarationForLinker() || isWeakForLinker());
    347   }
    348 
    349   /// This method unlinks 'this' from the containing module, but does not delete
    350   /// it.
    351   virtual void removeFromParent() = 0;
    352 
    353   /// This method unlinks 'this' from the containing module and deletes it.
    354   virtual void eraseFromParent() = 0;
    355 
    356   /// Get the module that this global value is contained inside of...
    357   Module *getParent() { return Parent; }
    358   const Module *getParent() const { return Parent; }
    359 
    360   // Methods for support type inquiry through isa, cast, and dyn_cast:
    361   static bool classof(const Value *V) {
    362     return V->getValueID() == Value::FunctionVal ||
    363            V->getValueID() == Value::GlobalVariableVal ||
    364            V->getValueID() == Value::GlobalAliasVal;
    365   }
    366 };
    367 
    368 } // End llvm namespace
    369 
    370 #endif
    371